Microstructure and hydrogen storage properties of Zr-based AB2-type high entropy alloys

This paper reports the partial substitution of Fe, Co, Ni and Cu for Mn in ZrMnCr0.5V0.5 alloy with to obtain ZrMn0.5Cr0.5V0.5M0.5 (M = Fe, Co, Ni and Cu) high entropy alloys. These alloy samples are prepared by electric arc melting, and their microstructure and hydrogen storage properties are investigated in detail. Structural analysis results show that all the five alloys consist of C14 type Laves primary phase. Metastable cubic phase can be observed in ZrMnCr0.5V0.5 and Fe-, Co-substituted alloys, while ZrNi, Cu10Zr7 and Cu8Zr3 phase secondary phases exist in Ni- and Cu-substituted alloys. Hydrogen storage testing results show that elemental substitution greatly improves the first activation properties of the alloys. All the five alloys can absorb hydrogen rapidly when the temperature is above 100 ℃, while the elemental substitution significantly affects the hydrogen absorption kinetics at lower temperatures. Compared with other four alloys, the Cu-substituted alloy has two kinds of Cu-Zr secondary phases, resulting in a poorer hydrogen absorption performance. Pressure-composition isotherms (P-C-T) test results show that all these alloys have very sloping absorption and desorption plateaus. It is also found that all the alloy particles are pulverized spontaneously during hydrogenation cycles, but there is no clearly change on phase structure of C14 type Laves phase, and the alloys show a good cycling performance. Among these alloys, the ZrMn0.5Cr0.5V0.5Fe0.5 alloy has the best hydrogen storage performance because it has the shortest activation time and fast hydrogen absorption at room temperatures.